A second major source of information consists of the ethnographic studies made within the past fifty years, among which should be mentioned the works of Kroeber, Merriam, Schenck, Gayton, and Gifford. These investigators depended principally upon informants who were elderly people in the decades from 1900 to 1940. Their memories, together with their recollection of what had been told them by their parents, carry back, on the average, to the period of the American invasion or just before it. Hence their knowledge of truly aboriginal population would be valid for the hill tribes only; yet data derived from them for that region is probably more accurate than can be obtained from the general estimates made by contemporary white men. These two types of information, contemporary American accounts and modern ethnographic material, can thus be used to supplement and check each other for the era of 1850. For conditions in the valley before 1840 we have to depend almost exclusively upon the historical records left by the Spanish and Mexicans. These consist of a series of diaries, reports, and letters, by both laymen and ecclesiastics, together with baptism lists and censuses from the coastal missions. This array of documents is to be found in the manuscript collections of the Bancroft Library of the University of California at Berkeley. It will be clear from these considerations that the population of the San Joaquin Valley can be determined with some degree of accuracy at two stages in the history of the region. The later period is at the point of intense occupancy by the Americans, at or near the year 1850, for here may be brought to a focus the data from both contemporary counts and the research of modern ethnographers. The earlier is for the epoch just preceding the entrance of the Spanish into California, or just before 1770. To assess the population at this period it is necessary to bring to bear information from all sources, American and Spanish, and to utilize all indirect methods of computation which may be appropriate. As a matter of historical interest, as well as to provide a background for the estimate of aboriginal population, the state of the natives in the period of the Gold Rush will be first examined. THE POPULATION OF THE SAN JOAQUIN VALLEY IN APPROXIMATELY 1850 CONTEMPORARY ESTIMATES AND COUNTS FOR THE ENTIRE REGION